Work

Coupled multiscale paleoclimate reconstruction with four-dimensional variational data assimilation

Year: 2026

Type: preprint

Abstract: Paleoclimate archives extend climate knowledge beyond the instrumental era, registering different seasons, variables, time averages, and memory lengths. A longstanding problem is to integrate these heterogeneous sources of information within a unified methodology. Here we present a new data-assimilation framework, Last Millennium Reanalysis 4D-Var (LMR4D-Var), which reconstructs climate trajectories from these heterogeneous datasets while balancing errors in the model, observations, and initial conditions. We compare results using LMR4D-Var to assimilate proxies from PAGES2k, Temp12k, and borehole temperature profiles without treating them as instantaneous equivalents. Instrumental verification shows that LMR4D-Var achieves the highest skill compared with previous reconstructions. Borehole assimilation preserves skill against withheld annually resolved records, increases agreement between reconstructed 300--2000-m ocean heat content and independent estimates, and yields a cooler reconstructed Little Ice Age ocean. Results for Temp12k demonstrate assimilation of decadal-to-millennial records and the potential for Holocene and deeper-time applications with suitable emulators.

Source: arXiv (Cornell University)

DOI: 10.48550/arxiv.2608.19469

Authors: Meng, Zilu, Hakim, Gregory J., Emile-Geay, Julien, Gondhalekar, Tanaya, Steig, Eric J.

Institutions: University of Washington, University of Southern California

Language: English

Topic: Geology and Paleoclimatology Research

Subfield: Atmospheric Science

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDG: Climate action

Open Access status: green

Funders: National Science Foundation, St. Francis Xavier University